1. Field of the Invention
The present invention relates to a method of and apparatus for processing a virtual local area network (VLAN) tag frame, and more particularly, to a method of and apparatus for processing a VLAN tag frame, wherein an upper switch device directly controls a terminal that is connected to a slave in a general data transmission system.
The present invention is derived from a research project supported by the Information Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) and the Institute for Information Technology Advancement (IITA) [2006-S-060-02, OTH-based 40G Multi-service Transmission Technology].
2. Description of the Related Art
An Ethernet bridge interconnects two or more local area networks (LANs). A port of a bridge may be connected to another bridge, or may be directly connected to a terminal or a router. Because the bridge processes a data link layer (layer 2), the bridge regards a router that processes a network layer (layer 3) as a general terminal. A port of the bridge may also be connected to a one-to-one link or a bus LAN sharing a bus. When an Ethernet frame is to be transmitted, a media access control (MAC) address of a destination (referred to as a destination address (DA)) is located at a front portion of the Ethernet frame and a MAC address of a source (referred to as a source address (SA)) is located next to the DA.
When a data frame is received, a basic function of the bridge is to transmit the data frame to a port that is indicated by a DA of the data frame. Whenever a data frame is received, the bridge learns that an SA of the data frame indicates an input port from which data frame is received, by binding the SA with the input port in an internal filtering data base (FDB) table. Also, the bridge looks up an FDB table entry corresponding to a DA of the data frame, reads the FDB table entry, determines a port that is connected to a destination of the DA, and transmits the data frame to the port. Information on the DA is learned when a data frame having the DA as an SA is received. If a data frame having DA information that has not been learned is received, the data frame is broadcasted to all ports except a port from which the data frame is input, in order to perform data communication. Also, if the DA indicates the port from which the data frame is input, it is considered that the data frame has already been transmitted to the destination and the data frame is disused. As such, terminals and routers which are connected to each other via the bridge, may communicate with each other by using MAC addresses, although they do not know physical locations of opposite parties. In a LAN, if a DA is a broadcast address, a data frame is broadcasted to all segments and, if the bridge does not know a destination, the data frame is flooded to all ports. The bridge checks entries of the FDB and removes an entry corresponding to an SA from which no data frame is input, in order to prevent a problem occurring when data communication is not performed by transmitting a data frame, which is to be transmitted to a certain terminal, to a wrong port due to old information, even though a position of a port of the terminal is changed in view of the bridge. As such, communication may be restarted in a short time by flooding the data frame after the entry is removed and obtaining responses from the destination received the flooded data frame. In general, if no data frame is input from a port that is indicated by a MAC address as an SA, an entry of the MAC address is removed; this process is referred to as an aging process.
The LAN connected via the bridge may be divided into a plurality of virtual local area networks (VLANs). In this case, only terminals included in the same VLAN are connected to each other and terminals included in different VLANs are not connected to each other. The VLANs are used in order to reduce traffics of a whole network by blocking a data frame to be broadcasted between LAN segments which do not need to communicate each other, when the LAN connected via the bridge becomes large, or to restrict transmission of a data frame to a certain group due to security reasons. When the VLANs are used, an Ethernet frame has a mark indicating which VLAN the Ethernet frame belongs to. Such mark is referred to as a VLAN tag. The VLAN tag includes a priority and a VLAN identification (VID) of the Ethernet frame. A bridge providing a VLAN function knows which port is connected to each VLAN. Thus, when a data frame is broadcasted to a certain VLAN, the data frame is broadcasted only to a port group that belongs to the VLAN. A terminal may insert a VLAN tag into a data frame. However, the VLAN tag is inserted into a data frame in a LAN. In general, the VLAN tag is inserted into a data frame based on ports or protocols at an entrance of the LAN. The LAN connected via the bridge is divided into the VLANs in accordance with a predetermined rule. The rule may be manually set for each bridge. Alternatively, the rule that is set for a bridge by a generic VLAN registration protocol (GVRP) may propagate through all bridges which are connected to the LAN, and thus each bridge may know which port is a member port of which VLAN. One port may be a port member of a plurality of VLANs.
In accordance with International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) G.984 gigabit passive optical network (GPON) standards, a port ID is included in a header region of a GPON encapsulation module (GEM) for transmitting a variable length packet, and is used as 4096 unique traffic identifiers for traffic multiplexing. A conventional GPON master in accordance with the above standards may identify a terminal below an optical network terminal (ONT) by using the port ID. However, an upper switch may not find out an identifier of the terminal.